Aircraft are commonly equipped with Cabin Pressure Control Systems (CPCSs), which maintain cabin air pressure within a desired range to increase passenger comfort during flight. A typical CPCS may include a controller, an actuator, and an outflow valve. The outflow valve is typically mounted on a bulkhead of the aircraft or on the outer skin surface of the aircraft, and selectively fluidly couples the aircraft cabin and the atmosphere outside of the aircraft. During operation, the controller commands the actuator to move the outflow valve to various positions to control the rate at which pressurized air is transferred between the aircraft cabin and the outside atmosphere, to thereby control the pressure and/or rate of change of pressure within the aircraft cabin. The controller may be configured to command the actuator to modulate the outflow valve in accordance with a predetermined schedule or as a function of one or more operational criteria. For example, the CPCS may additionally include one or more cabin pressure sensors to sense cabin pressure and supply pressure signals representative thereof to the controller. By actively modulating the outflow valve, the controller may maintain aircraft cabin pressure and/or aircraft cabin pressure rate of change within a desired range.
In some aircraft, the outflow valve may be positioned on the aircraft outer skin surface such that when pressurized air is exhausted from the cabin, the exhausted air may provide additional forward thrust to the aircraft. Thus, outflow valves may sometimes be referred to as thrust recovery valves. Modern thrust recovery valves often contain two valve door elements to optimize the forward thrust that is created. Because of the pressure difference between the pressurized aircraft cabin and the outside atmosphere, and because of the potential energy of the pressurized air in the aircraft cabin, some thrust recovery valves have a rather distinctive shape. This shape accelerates the air as it passes between the thrust recovery valve door elements to provide a net aft thrust force.
Although outflow valves, such as the one described above, are generally safe, reliable, and robust, these valves do exhibit certain drawbacks. For example, many outflow valves may be prone to noise generation, such as a “whistle,” especially at aircraft altitudes where the outflow valve may be near a closed position, but not in a sonic airflow regime. This noise can be irritating to aircraft passengers. Presently, such noise elimination is addressed by empirically adding several rows of variously sized vortex generators to various portions of the outflow valve. This, however, can increase overall valve complexity, weight, and cost.
Hence, there is a need for a cabin pressure outflow valve that eliminates irritating noise generation throughout aircraft altitude variations, without introducing unwarranted complexity, weight, and cost. The present invention addresses at least this need.